Preparation of organosilicon halides



reaction.

amount of'unreacted hydrocarbon halide presentin the condensed reaction 2,380,999, I mrmrron or ORGANOSILIOON mamas Murray M. Sprung, Booth, Schenectady, N.

Company, a

11m, Electric The present invention relates to thepreparation of organosilicon halides. It is particularly concerned with the preparation of organosilicon halides by infecting reaction between hydrocarbon halides and heated silicon in the presence of an inert atmosphere.

In the copending application of Eugene G. Rochow, Serial No. 412,459, filed September 28, 1941, and assigned to the same assignee as the present invention, is disclosed and broadly claimed the method of preparing organosilicon halides, more particularly, hydrocarbon-substituted silicon halides which comprises bringing a hydrocarbon heated silicon.

The present invention is based on our discovery that ifthe hydrocarbon halide in vapor form is brought into contact with the heated silicon in the presence of, i. e., mixed with, an inert gas such as nitrogen and the reaction between the silicon and the hydrocarbon halide component of the halide into contact with the above-mentioned Rochow application, certain unexpected results are obtained. The useof an inert gas in this manner permits better control of the reaction and minimizes the formation of undesired byproducts. In general, at a given temperature, better yields of hydrocarbonsubstituted silicon halides, such as the di(hydrocarbon-substituted) silicon halides wherein R is a hydrocarbon radical and X is a halogen atom, are obtained from the reaction between a hydrocarbon halide RX and silicon when the reaction is carried out in the presence of an inert diluent. This desirable result is usually acgas mixture otherwise allowedto proceed in accordance with the teachings of' UNITED 3mm PATENT 1 omen and William r. on-

Y., assis'nors to General corporation of New York No Drawing. Application March 4, 1942. Serial No. 433,293

9 Claims. (CL 2M0?) companied by a decrease in the amount of lowboiling reaction products, such as the chlorosilanes, SiHCla and SiCh, etc., formed during the In some instances, an increase in the state or it may be passed over, or bubbled through, a reservoir of a liquid hydrocarbon halide held at any desired temperature. With many of the hydrocarbon halides, this latter method, in which the nitrogen also functions as a carrier for the reactive hydrocarbon'halide vapor, is preferred since the rate of flow of the These contact masses and their gaseous mixture throughthe apparatus can be controlled by regulating the rate of flow of nitrogen into the reservoir while the amount [of the reactive hydrocarbon halide carried into contact with the heated silicon by the inert gas can be controlled by varying. the temperature of the hydrocarbon halide reservoir, i. e., the vapor pressure of the hydrocarbon halide. Although the inert gas may be mixed with the halide reactant in all proportions, best results are obtained when the inert gas comprises at least 25 per cent, preferably per cent, of the gas mixture. I

In'order that those skilled in th-artbetter may understand how the present invention may (a) A quartz reaction tube. was filled with a solid, porous silicon-copper contact mass prepared from a mixture of 90 parts silicon and 10 parts copper powders, pressed into pellets and sintered in hydrogen. at 1050? C. for 1 hour. preparation are more fully described and claimed in the copending application of Wlnton I. Patnode, Serial No.

412,461, filed September 26, 1941,. and assigned to the same assignee as the present invention. The preparation of organosilicon halides utilizing solid, porous contact masses of this type is disclosed and claimed in the copending application of Eugene G. Rochow and Wlnton L'Patnode, Serial No. 412,460, filed September 26, 1941, and assigned to the same assignee as the present invention. The tube was heated to a temperature of 300 through the tube at a rate of 80 c. e. per minute for 17 hours. The efliuent reaction products were passed through a trap cooled by a mixture .of dry ice and acetone. After the condensate collected in the trap was distilled to remove volatile materials boiling below 25? 0., there was oh- This higher-boiling portion was distilled using aprecision fractioning column and was found to contain 73.5 per cent dimethyldichlorosilane (CI-1ahSiCl-z, 9 per cent methyltrichlorosllane' CHsSiGla, about -6 per cent trimethylchlorosilane (CHshSlCl, and small amounts of other methylchlorosilanes. v

(B) Using, the same apparatus mntact mass, and temperatures as .were employed in-part (A) of this example, a mixture of methyl chloride and dry, oxygen-freenitrogen was passed over the C. and'methyl chloride waspassed the methyl chloride.

or checks all or some of the 'ute. When the silico I action'took place ciilc hydrocarbon halides bromide,

heated contact mass for 26 hours at the rate-t 40 c. e. per minute of the former and 100 c. 0. per minute or the latter. The condensate contained 207 grams of liquid boiling above 25' C. which, on fractional distillation, 86.5 per cent dimethyldichlorosilane, 4.0 per cent methyltrichldrosilane, and small amounts of other methylchlorosilanes. Thus the use of the inert diluent resulted in an increase of about 13 per cent in the yield of the dimethyldichlorosilane. The reason in the relatiye prodimethyldichloro product obtained of an inert atmosphere is not clearly It may be due to a shift in the complicated chemical equilibrlaset up during the process of synthesisor, more simply, it maybe due to the prevention of local overheating. In this connection it may logically be assumed that the formation of a symmetrical alkylhalogenosilane such as dimethyl dichlorosi lane from methyl chloride and silicon may most simply be represented by the equation:

2CHsCH-Si (CH3) zSiCh and that the formationof the otherhydrocarbon silicon chlorides such as the monoand trimethyl silicon chlorides CHsSiCla and (CH3) :SiCl, and silanes such as SiHCh, SiHzClz, looked upon this basis the presence of an inert atmosphere apparently favors the formation of the symmetrical product and retards side reactions. In the following example the inert gas func- .tions not only as a means for controlling the hydrocarbon halidesilicon reaction but also as a' carrier tor the hydrocarbon halide vapor.

Example 1.!

Dry-oxygen-iree nitrogen gas was bubbled through a-reservoir of ethylene chloride at the rate of 300 c. 0. per minute and then passed into filled with the same contact mass Example I. The temperature of the ethylene chloride was maintained at a temperature of 25-2'7 C. with the result that the now ethylene chloride vapors into the rate o1 0.5gm'. per min- -copper contact mass was heated toatemperature of HO-80C. a rapid rewith very little localized overheating or carbonization or the contact mass. The high-boiling siliconcompounds recovered from the condensed reaction products by-condensation in--a trap cooled by. an ice-water mixture contained a considerable quantity of 1,2 bis(trichlorosilyb' ethane. and their preparation are more fully described and claimedinthe copending application of Winton, 1-. Patnode and Robert W. 'Schiessler,- Ser iai No; 433-,328,-fl1ed conc rrently herewith and assigned to the same assignee as the present invention. It is to be unde tion' is not limited of nitrogen carriedthe reaction tube at cod. 9 cou to reactions involvingthe spenamed in the above llushydrocarbon halmentioned in silicon at the presence of an inert atmosphere with comparable results are the higheralkyl halides, e. g:, ethyl chloride,.ethy'l prowl chloride, etc; the aryl halid trative examples. Examples of specifically asaop oo other than copper metal.

The preferred reaction temperahires at-which substantial yields of the desired organosilicon halides are obtained depend,

in general, on the reactant or reactants, the particular catalyst (it any) used, and the specific re- 1 action conditions employed. 'In general, the use action at an elevated temperature chloride component of a mixture that our inveneither with the silicon or 1 gen through of the, inert gaspermits the utilization of somewhat higher reaction temperatures than when such ga'sisnot used.

Although nitrogen has been used in the above example'sfitis to be understood that other inert gases, 1. e. gases that do not react appreciably the hydrocarbon halide underthe conditions employed, may be substituted hr the nitrogen. Argon, helium, methane, are suitable substitutes. Nitrogen, because of its 1. The method con and a halogenated hydrocarbon in the presence of an inert gas. v

2. The method which comprises eflecting reaction at an elevated temperature between silicon and the alkyl halide component of a mixture comprising an inert gas and an alkyl halide in the presence of a metallic catalyst.

3. The method which comprises efiecting reaction between the hydrocarbon halide com ponent 0! a mixture comprising nitrogen and a heated silicon in the a copper catalyst for the reaction.

eflectin rehydrocarbon and silicon. in the presence of a metallic catalyst at an elevated temperature.

5. Themethod which comprises eflecting reaction between heated silicon and an alkyl halide in the presence of nitrogen.

and the methyl between heated silicon of nitrogen and action methyl chloride.

'1. The, method which comprises eilecting reaction between silicon and the alkyl halide conmixture of nitrogen and an alkyl from the group cc of and bromides, the said reaction out at an elevated temperature in the presences! a. ccpper catalyst.

8. The method of increasing the proportion of dimethyldichlorosilane resulting from the reaction. oivmethyl chloride with heated silicon, which comprises "introducing nitrogen into the methyl chloride prior to the react on thereof withthe-sllicon. 9. Theme od which comprlsespassins nitroa-reser-voir ota liquid hydrocarbon halide. adjustin voir to obtainthe desired ratio of nitrogen to hydrocarbon halide in the eilluent gas mixture, Passing said mixture over heated silicon and condensing the of reacalkyl chlorides temperatures, 1. e. the

the temperature oi! said. reser- 

